(a) Field of the Invention
This invention relates to aryl phosphite latent acid catalysts which provide controlled work time for hardening phenolic resins at ambient temperature and which can provide extended work times at ambient temperature with rapid cure at modestly higher temperatures. The phenolic resins are those which are hardenable by strong acids at ambient temperature.
(b) Description of the Prior Art
Phenolic resins can be cured (hardened) at ambient temperatures of about 16.degree. C. to about 38.degree. C. by: using strong acids such as phosphoric or sulfuric acids; organic esters at pH of about 12 to 13 (ester cure process); or by using lightburned magnesium oxide, with or without, an organic ester at pH of about 8.5 to 9. Hardening with strong acids has major limitations, i.e., difficulty to control, cannot easily afford extensive ambient temperature stability prior to hardening, creates corrosion problems and are very unstable when furfuryl alcohol is employed with the phenolic resin.
The ester cure process is generally characterized by high water contents such as that of up to about 50% in the resin and very high alkali contents with about 8% potassium ion being typical. High alkali ion content is unsuitable for preparation of polymer concretes using siliceous aggregate or as a binder for refractory composites, and results in high leachability upon exposure to water. The high water content, when the highly alkaline resin is used at levels well above the 5% to 15% based on aggregate normally used in foundry applications, affords composites with decreased density and can be characterized by undesirable exudate since they bleed liquor.
Ambient temperature curing, also referred to as ambient temperature hardening, using organic ester and lightburned magnesium oxide as hardener has several important shortcomings relative to the process of the instant invention. These shortcomings include: use of three components instead of two; work time, i.e., mix life, is very limited even in the presence of retarders; and only a very limited cure is obtained after 24 hours of room temperature hardening. This limited cure can lead to thermoplasticity at temperatures of about 60.degree. C. to 80.degree. C. after room temperature hardening and it cannot be devoid of metal ions. The two component system which uses lightburned magnesium oxide without ester as hardener has many of the same shortcomings as that of lightburned magnesium oxide with ester.
It has now been found that the aryl phosphites of this invention are particularly effective hardening agents for both ambient temperature hardening or rapid hardening at relatively modest elevated temperatures such as those of from about 50.degree. C. to 100.degree. C. or less such as from 50.degree. C. to 80.degree. C.